Magma fragmentation in highly explosive basaltic eruptions induced by rapid crystallisation

Fabio Arzilli, G. La Spina, Mike Burton, Margherita Polacci, Nolwenn Le Gall, Margaret Hartley, Danilo Di Genova, Biao Cai, Nghia Vo, Emily Bamber, Sara Nonni, Robert Atwood, Ed Llewellin, Richard Brooker, Heidy Mader, Peter Lee

Research output: Contribution to journalArticle (Academic Journal)peer-review

33 Citations (Scopus)
59 Downloads (Pure)


Basaltic eruptions are the most common form of volcanism on Earth and planetary bodies. The low viscosity of basaltic magmas inhibits fragmentation, favouring effusive and lava-fountaining activity, yet highly explosive, hazardous basaltic eruptions do occur. The processes that promote fragmentation of basaltic magma remain unclear, and are subject to debate. Here, we use a numerical conduit model to show that rapid ascent of magma during explosive eruption produces large undercooling. Novel in situ experiments reveal that undercooling drives exceptionally rapid (~minutes) crystallisation, inducing a step-change in viscosity that triggers magma fragmentation. Experimentally-produced textures are consistent with products of basaltic Plinian eruptions. We apply the numerical model to investigate basaltic magma fragmentation over a wide parameter space and find that all basaltic volcanoes have the potential to produce highly explosive eruptions. The critical requirements are initial magma temperatures lower than 1100 °C, in order to reach a syn-eruptive crystal content of > 30 vol.%, and thus a magma viscosity ≥ 105 Pa s, which our results suggest is the minimum viscosity required for the fragmentation of fast ascending basaltic magmas. Our study provides both a demonstration and explanation of the processes that drive basaltic Plinian eruptions, revealing how typically effusive basaltic volcanoes can produce unexpected highly explosive, and hazardous, eruptions.
Original languageEnglish
Pages (from-to)1023–1028
Number of pages9
JournalNature Geoscience
Early online date21 Oct 2019
Publication statusPublished - Dec 2019


  • Petrology
  • Volcanology


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